Optogenetic manipulation of brain reward. Direct electrical stimulation in the lateral hypothalamus (LH) is highly rewarding. The rewarding effects of LH stimulation are potentiated by drugs of abuse that directly or indirectly increase dopaminergic activity, whereas dopaminergic antagonists or lesions of dopaminergic neurons greatly attenuate such stimulation. However, different parametric studies have ruled out that the primary source of reward is direct depolarization of dopaminergic fibers at the tip of the electrode. Therefore, studies aimed at identifying the source of stimulation within the medial forebrain bundle will yield essential information about the components of the brain reward circuitry. The hypocretins (Hcrts), also known as orexins, are two neuropeptides derived from a single precursor, produced in a few thousand neurons in the LH. The hypocretins are essential to maintain arousal, as lack of hypocretin function results in narcolepsy. We and others have recently demonstrated that hypocretins may also be involved in brain reward function. Thus, Hcrt-1 can reinstate cocaine seeking behavior, and hypocretin receptor antagonists can block stress-induced reinstatement. Hypocretin neurons are also known to innervate dopaminergic neurons in the VTA and to induce glutamatergic plasticity in those synapses. We have recently developed a novel optogenetic method to selectively stimulate Hcrt neurons in vivo with millisecond precision by using a lentivirus expressing channel rhodopsin ChR2 under the control of the Hcrt gene promoter. Under this proposal we will use this optogenetic technology to determine whether the hypocretinergic system is an important component of the self-stimulation circuitry. In particular we will test: 1) whether rats press levers for optogenetic stimulation of Hcrt neurons (10 msec pulses, 20Hz, 10 sec, 20 mW) in the hypothalamus;2) whether rats show preference for different photostimulation frequencies of Hcrt neurons (20 Hz vs 1 -5 Hz). These two behavioral paradigms will be tested in wild-type and Hcrt-deficient rats. By using a state-of-the-art technology, these experiments will determine whether Hcrt excitation is an important component of the brain reward system, and may lead to new ways to analyze individual components of this system with unprecedented cellular specificity and temporal resolution. This proposal is directly responsive to the call of NIDA for new technology development relevant to drug addiction. PUBLIC HEALTH RELEVANCE: This proposal will use state of the art methods to identify neuronal structures involved in brain reward function.